Delayed coking is a relatively common process in which heavy fuel constituents are converted into lighter products (e.g., gasoline or diesel) using relatively harsh conditions (e.g., temperatures above 900° F.) over a period of between about 18–24 hours. The coking process is typically carried out in large coke drums, often 27–29 feet in diameter and approximately 130 feet in height. To ensure continuous operation, refineries normally operate multiple coke drums, wherein at least one coke drum is coking while at least another one is decoked.
In a typical coking vessel configuration, hydrocarbonaceous feedstock is fed from a pipe through the bottom flange of the coke drum and a blind flange is bolted onto the coke drum's upper flange during the delayed coking process. Once the coking process is complete and the coke drum has been quenched and cooled, the blind flange and the bottom head of the drum are disconnected from the vessel to cut and remove the coke. Due to the operating conditions in the coking vessel, manual removal of the blind flange and the bottom head has traditionally been time consuming and hazardous to operations personnel, especially because of the hazardous vapors and pressurized steam that may escape from the upper flange and/or lower opening of the coke drum during removal of the blind flange and the bottom head.
The deheading operation during the delayed coking process has been replaced in some instances by fully automated devices such as U.S. Pat. No. 5,221,019 to Pechacek, et al., U.S. Pat. No. 6,264,829 to Antalffy et al., U.S. Pat. No. 6,113,745 to Antalffy et al., U.S. Pat. No. 5,846,034 to Martin et al., U.S. Pat. No. 5,785,843 to Antalffy et al., U.S. Pat. No. 5,628,603 to Antalffy et al., and U.S. Pat. No. 5,098,524 to Antalffy et al., which address the removal of the bottom head or cover of a coke drum. Similarly, removal of the blind flange has been automated as described in U.S. Pat. No. 6,228,225 to Meher-Homji (All U.S. patent references incorporated by reference herein).
While automation of deheading operations in a petroleum coking unit considerably reduces risk of personal injury to operating personnel, new difficulties may arise. Most significantly, a remote operator is may inadvertently open a coking vessel while the vessel is still operating or not completely quenched since the operator is less acutely aware of the state of the coke drum process cycle. For example, if a hatch, or head, is too hot for an operator to manually remove fasteners safely, then the drum is probably still in service, and should not be opened. However, if the hatch or head removal is automated and remotely operated, and controlled by a unit that controls multiple drums, then the possibility exists the an operator could inadvertently open a drum in service.
Therefore, although various configurations and processes are known in the art to unhead a coking vessel, all or almost all suffer from one or more disadvantages. Thus, there is still a need for improved configurations and processes for safety locks, and especially for safety locks for a blind flange and/or bottom head of a coking vessel.